Flight, July 1934

THE AIRSPEED "ENVOY"High Speed, Retractable Undercarriage and Long Range are among the Chief Features of the Latest Production of Airspeed, Ltd.

IN the early part of last year Flight published the first detailed account of the Airspeed "Courier." This was the first British aeroplane to use a retractable undercarriage with all its attendant advantages. The "Courier," as will be seen from that description (March 23, 1933, page 266), was a successful attempt on the part of Mr. N. S. Norway and Mr. A. Hessell Tiltman to provide an aeroplane having a high cruising speed but which was economical to operate. Since that time a considerable number of "Couriers" have been built, and recently the 277 h.p. Siddeley "Cheetah" engine has been fitted instead of the "Lynx," thus raising the cruising speed to 150 m.p.h. Now, in response to a demand for a machine of rather better performance, but with the added safety of two engines, the "Envoy" has been produced. The first of these has been built, with Wolseley engines, to the order of Lord Nuffield for the England-Australia race. Others of the type are under construction, and one, designated the A.S.8, which will have supercharged "Cheetah" engines, will be flown in the race by Capt. T. N. Stack. As is usual with an aeroplane of this size for commercial purposes, the cabin accommodation may be varied to suit the purchaser. This first model will have seats for six passengers and one pilot. Obviously, by varying the number of passengers the amount of fuel carried may be altered and the range increased or decreased accordingly. With six passengers the tanks hold sufficient for a range in still air of 403 miles. Structurally the "Envoy" differs but little from the "Courier." In fact, the outer wing-sections are interchangeable between the two types. Wings and fuselage are mainly composed of plywood and spruce. The covering of the latter is three-ply wood, and of the former, doped fabric. The front portion of the fuselage, forming the cabin accommodation for the passengers and pilot, is practically of monocoque construction, with a three-ply skin. Particular care has been taken to ensure that the passengers do not suffer from lack of light or ventilation. In the pilot's cockpit all the front windows can be opened so that they can be cleaned easily during flight. The centre-section, upon which the fuselage is mounted and which forms the cabin floor, carries both engines, the fuel tanks and both sides of the retractable undercarriage. This centre-section is built up as a single unit, with very heavy bracing between the box type spars. The outer portions of the wings are attached to these spars by heavy steel bolts passing through vertical hinges, which are secured to the spars by means of laminated steel plates, so that the extension planes can be quickly detached. These planes are heavily tapered both in plan form and profile, the section used being Clark Y.H. suitably "stepped" to give the necessary taper. Special precautions have been taken to ensure a high degree of torsional rigidity in the wings, so that the whole structure is extremely stiff. The main-plane spars are of the box type of construction, with spruce flanges and three-ply webs. The webs are particularly interesting as the plywood used has the centre lamination double the thickness of those outside it. Moreover, this plywood is laid on the spar with the grain of the wood at 45 deg. to the spar axis. In this manner a high strength/weight ratio has been achieved. The wing ribs are of spruce, as is the drag-bracing system, which has been designed to provide a high degree of torsional stiffness. The wings and Frise type ailerons are fabric-covered. The retractable undercarriage is almost identical with that of the "Courier," and is extremely simple. The Vickers oleo-pneumatic compression strut is hinged to the front spar in the same plane as the bent axle. The radius rod running backwards to the rear spar is divided unequally, the short portion being in front. An oil cylinder is attached to the top of the rear spar, and in it is a piston with the piston rod attached to the front end of the longer portion of the radius rod. When the piston is withdrawn into the cylinder by means of oil pressure, the radius rod is bent and pulled upwards into the wind, carrying with it the undercarriage and about three-quarters of the landing wheel. This is arranged so that in cases of dire emergency on very rough ground the pilot could land a machine with the wheels in the retracted position, knowing that there would be no possibility of turning over on doing so. An electrical indicator system is fitted to tell the pilot the position of the wheels. The flying controls provided for the pilot consist of a control wheel and parallel-motion pedals for rudder operation, combined with a very neat form of rudder bias gear enabling the machine to be flown easily in the event of a failure of one engine. Tail plane trimming gear is provided which operates in the normal manner. The whole of the tail units are extremely clean in design, and while being efficient offer very little drag. Although there are no external bracing wires or struts, both the fin and tail are exceptionally rigid, and great care has been taken to eliminate any possibility of flutter in the tail plane or rudder by maintaining a high degree of torsional stiffness throughout the whole of the rear part of the fuselage.

Flight, January 1935

FOR FAST COMMERCIAL TRANSPORTThe Airspeed "Overseas Models,” with "Lynx IV.C" Engines: A Wide Choice of Equipment and a High Performance

KNOWN as the "Overseas Model," an improved version of the "Envoy" has recently been produced at the Portsmouth works of Airspeed, Ltd. It is fitted with two "Lynx IV.C" engines (240 h.p. at 2,090 r.p.m.), which give a top speed of 174 m.p.h. Basically, this "Envoy" is practically identical with that built for the late Mr. C. T. Ulm, and differs but little from the Wolseley-engined “Envoy” which was described in Flight of July 12, 1934. The cabin of this new model can be arranged either as a six- or eight-seater, and the performance in general considerably surpasses that of the previous machine. Certain structural alterations to the centre section of the wing have enabled the all-up weight to be increased to 5,850 lb., which means that, despite the extra weight of the larger engines, a usefully large payload is still permissible, with a long range. The well-known Airspeed retractable undercarriage is retained, and behind the engines are fairings very similar to those placed behind the "Cheetah" engines in the "Viceroy," which Capt. Stack flew in the England-Australia Air Race. The leading edge of the outer portions of the wings has now been completely covered with plywood extending from the top of the front spar around the leading edge to the bottom of the front spar, thus making a structure both rigid in torsion and so strong that it will not be damaged when pushed against while manhandling the machine. The cabin upholstery has been done, like that of so many of the well-equipped and comfortable aircraft nowadays, by L. A. Rumbold and Co., and in the model we tried the seats were very comfortable indeed. The general equipment is very full, with small folding tables and an ashtray for each seat. A Plessey A.C.44 wireless set is let into the after bulkhead of the cabin in a very neat manner, the remote control being contained in a very small box and mounted close by the pilot's right hand. Behind the after bulkhead is a spacious luggage compartment. The internal arrangements of the cabin can, of course, be varied to suit any individual operator's wishes, but the arrangement just described is one which should have a wide appeal for those whose flights are likely to be upwards of 400 miles. In the air the “Envoy” had all the attributes of a fairly heavily loaded high-speed machine - that is to say, in bumps the movement was comparatively hard, short, and sharp, but without producing any particularly disagreeable sensation in the passengers. Flaps have not been fitted, as the manufacturers feel that not only are the take-off and landing adequately short without their use, but that their incorporation would entail an increase of structural weight which would result in an undue decrease of payload. The take-off, considering that no flaps are fitted, is good; and, in the matter of landing, it must be remembered that the undercarriage, when in the lowered position, acts to a certain extent in the same manner as would flaps - that is to say, it increases the drag very considerably, and steepens the glide of the machine appreciably. Thus, although the "Envoy” is a clean machine with a high performance, it is still possible to land it off a steep approach over high obstacles. We did not, on this occasion, have the opportunity of piloting the machine, but from what we saw, and from the opinion of pilots who have flown it under both good and very bad conditions, it is clear that it retains all those most desirable characteristics which were embodied in the Airspeed "Courier," which was described in Flight of March 23, 1933. There is, of course, the usual tail-trimming gear, consisting of a screw-operated mechanism which alters the position of the leading edge of the tail plane; and, in addition, a rudder bias gear is fitted which enables the machine to be flown hands off with one engine cut out. Another refinement which many pilots will like is the aileron bias gear, whereby lateral trim can be altered, not only for single-engine conditions, but also to allow for the idiosyncrasies of pilots, the majority of whom fly with one wing slightly lower than the other. It is difficult to imagine any aeroplane which allows a better outlook from the pilot's cockpit. The deep, vee-shaped windows are at such an angle that they do not collect fine rain or snow, and are low enough to permit the pilot to look almost vertically below him. The large window in the front on his left-hand side is also split vertically, so that when the visibility is really bad half the window may be slid to one side, leaving an opening through which he can see clearly. About the operation of the retractable undercarriage we need say very little, as this has been described very fully in connection with previous Airspeed machines; the pump handle at the right-hand side is easy to work. This particular "Envoy" has been built for demonstration in India, and it left this week, via Spain, where Sir Alan Cobham, who was accompanying it, hopes to demonstrate. It will be flown by Flt. Lt. H. C. Johnson.

Flight, March 1936

WHEN the necessity for combining commercial efficiency with higher speeds inevitably drove designers to reduce drag as far as was practicable, it was obvious that some means had to be evolved for reducing this inspired cleanliness at will. No aerodrome in the world would be large enough - or, at least, sufficiently free from obstructions - for a machine in which the reduction of parasitic drag had been carried to its logical conclusion. With the arrival of the modern conception in high-speed transport machines, therefore, there came also the flap. Originally developed with the idea of increasing lift and thereby lowering the landing speed of machines with a high wing loading, flaps are looked upon by pilots, at least, almost entirely in the light of their capacity for steepening the approach. Certainly there can be few transport aeroplanes with an approach as steep as that of the latest Envoy with its split trailing-edge flaps lowered. Furthermore, this machine can be brought in safely at a speed which would hardly be credited by anyone who had not actually watched the A.S.I. Translated into bald figures, the stalling speed of the Series II has been reduced by 9 m.p.h. with the help of these flaps, and the landing run has been reduced by 50 per cent, or thereabouts. In its unflapped form the Envoy stalls at an indicated 55 m.p.h.; the touch-down now takes place with the needle lying between 40 and 45 m.p.h. An average of twelve landings in a 5-m.p.h. wind gave, it is understood, a figure of 140 yards for the landing run. It was found, however, that the increased drag virtually balanced the increased lift during the take-off, which we roughly timed as taking 13 seconds in a 10-m.p.h. wind with a medium load. Unfortunately, the most pronounced effect of the flaps - during the approach - cannot be indicated with the assistance of figures, but can only be seen and felt. At a gliding speed of 60-65 m.p.h. this flapped approach can best be described as being as steep as that of a training type. At 50-55 m.p.h. it is even steeper, though the attitude of the machine is, of course, somewhat nose-high and the sink is pronounced enough to demand a little extra speed before holding off for the landing. Nor is any particular skill required for a short landing. Flt. Lt. C. H. A. Colman, of course, as the Airspeed demonstration pilot, can make the new Envoy do some very remarkable things, but, at the Heston demonstration last week, at least two pilots having no previous experience of the machine made approaches and short landings which would not have disgraced the pilot of a light aeroplane. Despite the many statements made by research experts, Mr Errington, the chief test pilot, claims that the flaps-down stall is quite innocuous and that the Envoy, which has in addition, rather pronouncedly tapered wings, does not tend to drop a wing even from a full stall. The loss of height, he says, is quite a lot less than in the case of the unflapped type - approximately 300 ft. as compared with 500 ft. indicated on a sensitive altimeter. If the machine is trimmed correctly for a 65 m.p.h. glide the effect of lowering the flaps is merely to depress the nose with no change in the indicated air speed. Aileron control remains down to the moment of stall. The normal hydraulic gear which is used for the retractable undercarriage is also used for the flap operation. It may be remembered that, on previous Envoys, a pump handle and a change-over lever are placed to the right of the pilot. With the Series II a third lever is placed on the pilot's left, beside the tail-trimming wheel; according to its position the normal "up or down" control and the pump handle operate either the undercarriage or the flaps. In the experimental model, at least, the flap position is indicated by means of a pointer on the right-hand side of the control cabin. In the air there is little chance that the pilot might make a mistake, since, with the undercarriage still up, the warning syren would indicate the fact as soon as the engines were throttled back, and, in any case, feel, sound and sight would tell him that the flaps, rather than the undercarriage, were being lowered. A very careless pilot might possibly pump the undercarriage up while the machine was on the ground, but in just the same way, he might also do a number of other foolish things in any aeroplane. One of the more interesting flying characteristics of the Envoy, incidentally, is that the take-off is best made tail down - with the trimmer wound well back. As soon as the machine leaves the ground the wheel can be wound forward again before attending to the undercarriage pump. The particular machine used for the demonstration was fitted with Wolseley Scorpio engines which, when turning over a t 2,200 r.p.m. gave a cruising speed of approximately 150 m.p.h. The Rotax electric starters were noticeably quiet and efficient in action. High performance for a modest power expenditure has been a feature of all Airspeed machines since Messrs. Tiltman and Norway first introduced the Courier some years ago. That machine, it may be remembered, was the first British low-wing monoplane to be fitted with a retractable undercarriage, and showed the way to still greater efficiency. The maximum speed of 173 m.p.h. with two Wolseley Scorpio engines corresponds to an Everling high-speed figure of 23.7, which must be regarded as good for a twin-engine type. At the same time the structural efficiency is good at 1.63, showing that, when equipped for passenger carrying, the Envoy carries as disposable load 63 per cent, of its own weight.

Flight, October 1938

British Commercial Aircraft

Airspeed

AIRSPEED

ONE of the first machines to be built according to the modern formula in this country, the Airspeed Envoy is in use over here on internal airlines and also abroad, notably in Australia and Japan. The Series III type, which is the latest of the Envoys, is normally fitted with Armstrong Siddeley Cheetah IX moderately supercharged engine, with which it has a cruising speed, at optimum altitude, of 170 m.p.h. - a figure which is often forgotten when the performance figures of more recent transport machines from abroad are being quoted. In its newer forms the Envoy is fitted with split trailing-edge flaps which extend from aileron to aileron and can be set to any angle up to approximately 80 degrees. The only fault which could be found with the original Envoys concerned the flat angle of approach, and this criticism certainly cannot be directed against the Series III type when the flaps are in the fully down position. The undercarriage is, of course, retractable, and the particular mechanism used is one of the most reliable yet devised and has been fitted to Airspeed machines ever since the Courier was produced in the company’s early days. The structure of this cantilever monoplane is of w'ood with a ply-stressed wing and semi-monocoque fuselage. Since the machine is in­tended for comparatively small-scale operations, there is accommodation for only one pilot, and when a radio operator is carried he takes one of the seats behind the forward bulkhead. Airspeed Envoy III data:- Span, 52ft. 4in.; length, 34ft. 6in.; all-up weight, 6,600 lb.; weight empty (including electrical and standard equipment and normal upholstery), 4,341 lb.; wing loading, 19.5 lb./sq. ft.; power loading, 9.4 lb. /h.p.; maximum speed at altitude, 203 m.p.h.; cruising speed at 62 1/2 per cent power at 10,000ft., 170 m.p.h ; service ceiling, 22,000ft.; single-engined ceiling, 6,250ft.; cruising range with normal tank­age, 620 miles; cruising range with auxiliary tankage, 1,000 miles. Makers: - Airspeed (1934), Ltd., The Airport, Portsmouth, Hants (Portsmouth 2444).

What the "Envoy" looks like on the ground. Landing lights are fitted in the leading edge of the wing of this machine, which was seen at the S.B.A.C. display at Hendon. The Wolseley engines are cowled with Townend rings.

SERVICE CEILING WITH FULL LOAD 24,000 FEET. Although it is not usual to fly at such high altitudes in Europe, a service ceiling, at such a height does ensure that the Envoy Series II at normal altitudes has a very good performance with a rate of climb and single engine performance which gives a wide safety margin in cases of emergency.

The optimum altitude for the Airspeed Envoy is 10,000 feet and at this height the cruising speed at 62 1/2 maximum power is 175 m.p.h. and the range 650 miles, with normal tankage. The maximum speed is 210 m.p.h.

It is recognised that the business demands of airline operators are for the lowest possible operating costs. Accordingly the Airspeed "Envoy" is of particular interest because its robust construction reduces maintenance to a minimum; its medium powered engines, coupled with aerodynamically clean design give 20 or 30 miles more distance per hour and it flies steadily in all weather conditions so that schedules can be maintained without time loss. Money and time is saved when "Envoys" are operated.

The Envoy Series II has ample power for operating from aerodromes situated at high altitudes. For instance, at 6,000 feet with Cheetah IX engines, the take-off run, in a 5 m.p.h. wind, is approximately 300 yards, whilst if one engine should cut out at this height, the aircraft will still climb on full load at the rate of 50 feet per minute. The safety margin of the Envoy Series II is, therefore, very high, and is another factor of interest to Airline Operators.

High speed cruising has been demonstrated very effectively recently by two Airspeed Envoys fitted with Wolseley Scorpio engines. Visiting the Stockholm Exhibition one machine covered 3,381 miles in 23 hours, without the engines being touched. Fuel consumption was 22 gallons per hour, oil consumption 2 quarts per hour. The engines were fitted with self starters and it was not even necessary to turn the propellers by hand to suck in.

IN THE FLOODLIGHTS: This photograph, taken by a Flight photographer at Heston during the Household Brigade display, gives some idea of the value of modern floodlighting equipment. Those at Heston, of course, are of Chance manufacture, and the machine is an Airspeed "Envoy"

The "Envoy" at Heston. From left to right can be seen Col. Boyle, Mrs. Anthony Eden, Ald. W. Hemmingway (the Mayor of Leeds), Ald. F.H.O'Donnell, Lord Grimthorpe (Chairman of North-Eastern Airways) and Col. Cameron.

AIR MARSHAL SIR PHILIP JOUBERT DE LA FERTE (Air Officer Commanding, R.A.F., India) and F/O King on the occasion of the Air Marshal’s visit to the Airspeed works to take delivery of the first of two Envoys for India

FOR PACIFIC FLIGHT: The twin-engined Airspeed "Envoy" monoplane, in which Mr. C. T. P. Ulm and Mr. G. M. Littlejohn propose to fly from Canada across the Pacific to Australia, being shipped at Southampton for Montreal.

Ansett Airway’s Airspeed Envoy (Wolseley Aries) over Melbourne, with the Shrine of Remembrance (which is quite near the Air Board H.Q.) in the background, and Government House to the left. This machine was originally owned by Lord Nuffield and was flown by Sqn. Ldr. Hilton from Capetown to Croydon in fast time.

The Airspeed ENVOY may be operated as a luxurious four-seat private owner aircraft, or as a six-seat, or eight-seat passenger aircraft. In both the four-seat and six-seat arrangement, a toilet is provided at the rear of the cabin. All are fitted with split trailing edge flaps and the Airspeed patent retractable undercarriage, the reliability of which has been tested thoroughly in all parts of the world.

The "Envoy" has been designed for high and economical cruising speeds. The Airspeed type of wood construction also ensures very low maintenance and C. of A. costs and has been thoroughly proved in the most varied climates from extreme cold to the humidity and heat of tropical countries.

Another long delivery flight PORTSMOUTH - HONG KONG emphasizes the reliability of the ENVOY. In fourteen days - during several of which no flying was possible owing to waterlogged aerodromes and bad weather - a Series III Cheetah IX Envoy has completed a delivery flight to Hong Kong. It was fully loaded to 6400 lb. and had a range of 1000 miles. This again proves the unfailing reliability of the Cheetah IX Envoy III.

THE KING'S ENVOY: One of the first flying views of the specially prepared Airspeed Envoy Series III (two Armstrong Siddeley Cheetah Xs) which is maintained for the transport of Royalty and State personages. The top speed is over 200 m.p.h. This particular machine belongs to the King’s Flight.

TRANSPORT RACING: The one machine in the South African race which is equipped as a long-distance machine should be equipped - Waller and Findlay's Envoy. In addition to the safety provided by two Siddeley Cheetah IX engines and full blind-flying equipment, this machine has Marconi two-way and D/F radio and carries a radio operator.

Airspeed. A.S.6E Envoy III OK-BAL, above, was one of four used by CSA on their service to Moscow, inaugurated on September 2, 1936. It ended its life in the Finnish Air Force, being damaged beyond repair on July 31, 1943.

Conversion from luxury air liner into fast medium bomber, by four men in eight hours, is the outstanding feature of the latest type Airspeed Envoys, as supplied to the Government of the Union of South Africa. The wisdom of equipping air line personnel with this type of aircraft is most apparent when it is realised that in peace time pilots will become thoroughly familiar, in all weather and load conditions, with the type of aircraft they would be called upon to fly in time of war.

PERFORMANCE and CONVERSION. The New Envoy is the first British aircraft built for rapid conversion from a commercial into a military machine with a performance equal to, if not belter than machines designed wholly for military purposes.

Were it not for the rear gunner's turret it would be impossible to distinguish this military version of the Envoy from its civil counterpart. The covered forward gun trough can be seen below the control cabin.

An important feature of the new Airspeed Convertible Envoys is the rapidity with which the aircraft can be converted from purely civil aeroplanes into fast bombers, or reconnaissance machines. This conversion can be carried out by four men in four hours and gives an additional value to high performance.

The maximum speed of the Convertible Envoy - 210 m.p.h. - is proportionately equalled by the speed with which the aircraft can be converted from civil into military form. The conversion is carried out by four men in four hours. Now that re-arming occupies such a prominent position in Government programmes, throughout the world, the Convertible Envoy is of particular interest.

The field of fire provided for the rear gunner can be visualised in this picture, which also shows the useful fact that the undercarriage, when retracted, can still be used for emergency landings on rough ground.

BRITISH ABROAD: One of the Japan Air Transport Company's Airspeed Envoys on the tarmac at Haneda airport, Tokyo. Routes covering some 652,500 miles in the year are now operated regularly by this company - including a service to Manchukuo.